"We were excavating near where the sonderkommando barrack was and we came across two rows of buried barbed wire," Polish archaeologist Wojciech Mazurek was quoted as saying by The Telegraph. "Digging down we found the traces of the tunnel. It was about as wide as a human, and we are 99 percent certain that it was an escape tunnel." [8 Grisly Archaeological Discoveries]

Sobibor was operated in German-occupied eastern Poland between 1942 and 1943. Estimates for the number of people killed there range from 167,000 to upwards of 250,000. Virtually all of the victims were Jews and most were gassed upon arrival. Some prisoners were spared immediate death and kept in the work units known as the sonderkommando, forced to help in the gas chamber operations and the disposal of bodies.

The researchers digging at the site reportedly don't have any evidence that the newly discovered escape tunnel was ever actually used. Prisoners at Sobibor did, however, stage an uprising in October 1943. Six-hundred prisoners revolted and managed to kill nearly a dozen of their guards. Many of the 300 laborers who broke out of the extermination camp were eventually captured and killed, and only 50 escapees are believed to have survived the war.

After the uprising, Nazi officials leveled the camp and covered its traces. That makes work difficult for archaeologists trying to understand the site.

"The area we were excavating has been disturbed and plundered many times over the years since the war," Yoram Haimi, an Israeli archaeologist who is also investigating the camp, was quoted as saying by Haaretz. "It's a mess containing human bones, human ash, glass, pieces of metal and a lot of waste."

Excavations have been underway at Sobibor for more than a decade. In addition to the escape tunnel, the team has reportedly found a crematorium, human skeletal remains, and dozens of artifacts including eye glasses, jewelry and sobering personal items, like a Mickey Mouse pin, that seem to have belonged to children.